Officials say COVID-19 antibody testing is crucial to reopening business — but what is it?

A lab scientist works to validate rapid antibody tests of COVID-19 samples
A Mirimus, Inc. lab scientist works to validate rapid IgM/IgG antibody tests of COVID-19 samples from recovered patients on April 10, 2020, in Brooklyn, New York City.
Misha Friedman | Getty Images

Last weekend, Jaime Kastner decided to get a test to see if he had been exposed to the new coronavirus.

The 54-year-old had been sick back in January with chest pain, shortness of breath and an intermittent fever.

“I was feeling bad enough to go to the doctor,” he said. At the time, coronavirus wasn’t on Kastner’s radar, and his doctor attributed his symptoms to stress.

Fast forward to this weekend, Kastner heard that a drug testing firm near his home in Plymouth, called Minnesota Monitoring, had just started offering rapid tests to detect COVID-19 antibodies — proteins the body produces to fight a virus, and a sign that someone has been exposed to the virus and recovered.

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“Curiosity got me,” said Kastner, who owns a fitness studio, which has been closed during Minnesota’s stay-at-home order. “I’m in a position where I’m around a lot of people in my studio. So, I wanted to be doing everything I can to keep my members safe and my family safe.”

Even though he had an inkling he might have had COVID-19 a few months ago, Kastner said he was surprised when his test came back positive for the antibody — not just once, but a second time.

Kastner’s experience is a data point in the growing demand for tests that might determine if someone has been exposed to COVID-19.

Mayo Clinic and the University of Minnesota have both launched antibody tests in recent days. And state officials are pointing to such tests as important tools as they consider how to reopen the economy. They may provide insight into how widespread the virus is, and how long it’s been here.

But simultaneously, state and local officials are issuing caution against a flood of tests on the market that may not be reliable or accurate, since the federal Food and Drug Administration has waived some of its regulations to get the test to the public quickly.

What is an antibody test?

Antibody tests determine whether you’ve already been exposed to the coronavirus by looking for proteins in your blood that your body created to fight it. If those antibodies are present in your blood, it’s a sign that you’ve already had COVID-19 — even if you didn’t experience severe symptoms, or any symptoms at all.

These tests are typically conducted with a finger prick or blood draw, and can be processed quickly. Some companies say their tests are only effective weeks after someone has been exposed, and the body has had time to mount a response to the virus.

Tests used to detect COVID-19 antibodies are different from the nose-swab diagnostic tests used to determine if someone is actively fighting the disease.

Those tests examine material gathered from a nasal swab on a possibly infected patient to detect the genetic information of the virus. They are only viable when someone is actively infected with the virus.

Who is offering the antibody tests — and who can get them?

Mayo Clinic and the University of Minnesota are ramping up antibody testing.

Both institutions say they have the capacity to conduct thousands of tests daily. But they’re starting small to focus on health care workers, people who have tested positive for the virus already, and people who likely had it but were never tested.

Mayo Clinic Laboratories president Dr. Bill Morice said that’s for a few reasons.

First, they want to make sure the tests work. But they’re also looking for people to participate in their convalescent plasma program, which holds promise as a treatment for COVID-19, and they don’t want to overwhelm the system out of the gate, in an effort to conserve supplies.

“We want to make the test, really as soon as possible, available to as many people as possible,” Morice said.

Meanwhile, at least one Minnesota company is offering an off-the-shelf test. For several days, Minnesota Monitoring has been selling a rapid antibody test distributed by Confirm BioSciences for $50 a patient.

Minnesota Monitoring president Karen Altman said that the company was nearly out of the first 500 tests it had ordered. She said they will be submitting all data about their test results to the state Health Department.

Why are state officials so interested in doing more of these tests?

The short answer is that Minnesota officials say knowing just how many people have already been exposed to the virus will help them reopen the state more quickly.

Antibody tests have the potential to provide valuable information about exposure — but operate under the assumption that exposure to the virus brings some immunity against getting it later. Because scientists still don't know much about the new coronavirus, that’s not yet certain.

Still, state leaders say that increased antibody testing and diagnostic testing will help them make better decisions about how to reopen the economy without putting people at risk.

The Walz administration says it’s working closely with Mayo, the University of Minnesota and other health care providers around the state to make that happen.

“We’re pretty optimistic that we can significantly ramp up in the very short run, which will start to give us a lot better picture of where we are at,” Gov. Tim Walz said on a call with reporters this week.

On the same call, Health Commissioner Jan Malcolm talked about also ramping up testing that can be done outside the laboratory — for instance, in drug stores.

Are the antibody tests accurate?

This is where messaging from the government gets muddy.

While officials on the state and federal levels are holding up antibody testing as a game-changer in terms of understanding how widespread the virus is, they’re simultaneously warning against a flood of tests on the market that may not offer reliable results.

The dissonance stems from a decision the Food and Drug Administration made in mid-March to waive initial review of the tests in an effort to get them to the public faster. So far, more than 70 companies have alerted the agency that they will sell tests in the United States.

But in the last few days, FDA officials have warned against inaccurate tests on the market, and said the agency will take action against companies making false claims or marketing tests that are not reliable.

One reason these tests may not be reliable has to do with the populations where they’re being used. If the disease is already widespread in a community, the tests are likely to produce better results.

But an antibody test is less likely to be accurate when few people in the community have been exposed to the virus, Morice said.

He said Mayo is working with trusted companies to develop its test, and it is very confident it works. By rolling them out slowly in the lab, he said, researchers were able to make sure the tests are reliable — and that they don’t produce a false positive if, for instance, they detect antibodies associated with another virus.

Meanwhile, the University of Minnesota has built its own test.

“It’s extraordinarily sensitive and specific, and we’ve tested this against hundreds of samples,” said Dr. Tim Schacker, vice dean of research at the University of Minnesota and an infectious disease physician. “If it’s positive then the patient really, truly is positive. If it’s negative, then the patient really, truly is negative.”

What should you do if you test positive for the antibody?

At this point, it’s unclear how individuals should responsibly use the results of an antibody test.

For his part, Kastner said he’s not entirely sure his result is accurate — even after he was tested twice.

“I’m still pretending like I’d never gotten the virus,” he said. “I’m not really sure what to do with the information.”

He’s wondering: Should he tell his gym members? Reassure his family?

While getting the result of an antibody test may be useful to government leaders in making big-picture decisions about letting people go back to work or reopening parts of the economy, it’s unclear how state officials would track or use data about positive antibody tests if widespread testing became available.

And scientists say that even if we can detect whether someone has produced an antibody response to COVID-19, a lot of questions remain.

“We’re in this place where we’ve got this test. But we don’t have a lot of experience with it,” Schacker said. “So, we don’t know what it means.”

For instance, scientists don’t know yet how much immunity someone needs to fight the virus, or if producing the antibody means a person won’t get it again.

The only thing testing reveals is whether someone has never had the virus, whether someone has had it and fought it off, or whether someone is experiencing the virus, Schacker said.

“There’s these unknowns,” Schacker said. “We don’t have the luxury of time to sit and figure this out the way I’d like to. We just have to decide what level of risk we are comfortable with, and go with it.”

COVID-19 in Minnesota

Health officials for weeks have been increasingly raising the alarm over the spread of the novel coronavirus in the United States. The disease is transmitted through respiratory droplets, coughs and sneezes, similar to the way the flu can spread.

Government and medical leaders are urging people to wash their hands frequently and well, refrain from touching their faces, cover their coughs, disinfect surfaces and avoid large crowds, all in an effort to curb the virus’ rapid spread.

The state of Minnesota has temporarily closed schools, while administrators work to determine next steps, and is requiring a temporary closure of all in-person dining at restaurants, bars and coffee shops, as well as theaters, gyms, yoga studios and other spaces in which people congregate in close proximity.

Correction (April 16, 2020): An earlier version of this story stated that Jaime Kastner sought a second test on the advice of his doctor. That has been corrected.